Space remains a classic extreme environment encompassing large radiation fields in addition to wide temperature swings; these environmental factors place stringent demands on technology platforms for use in space-based electronic systems.
Ionizing radiation can cause unwanted effects in semiconductor devices. These unwanted changes of state caused by ions or electromagnetic radiation striking a sensitive node in a micro-electronic device are known as single event upsets (SEUs). SEU mitigation is a major concern and an area of active research for this technology as a result of upset sensitivities to ion linear energy transfers as low as 1 MeV-cm2/mg for unhardened applications.
Current technology employs process modifications to radiation harden microelectronics. However, these technologies are typically expensive and lag in performance with commercial processes, and therefore, there is a need for developing radiation-hardening by design (RHBD) techniques. These techniques center on using circuit and layout optimizations to improve the circuit radiation response. This is discussed by G. Niu et al., IEEE Trans. Nucl. Sci., vol. 49, no. 6, pp 3107-3114, December 2002, R. Krithivasan et al., IEEE Trans. Nucl. Sci., vol. 50, no. 6, pp. 2126-2134, December 2003, and R. Krithivasan et al., IEEE Trans. Nucl. Sci., vol. 52, no. 6, pp. 3400-3407, December 2006.
A good candidate technology for these RHBD techniques is Silicon-Germanium Hetero-junction Bipolar Transistors (SiGe HBTs) due to their natural fit for extreme environment applications. SiGe HBTs are understood to be total-dose radiation tolerant due to: (1) the heavily doped, epitaxially grown, extrinsic base, (2) thin emitter-base (EB) spacer, and (3) compact and heavily doped active regions.
Microelectronic device and circuit designers have long sought to combine the superior transport properties and design flexibility offered by bandgap engineering using SiGe with the high yield and low cost of conventional Si fabrication. However, because of the difficulty in growing lattice-matched SiGe alloy on Si, this concept has only reached a sufficiently practical state over the last decade. With the introduction of epitaxial SiGe alloys, this capability has finally been achieved.
Notwithstanding SiGe HBT applicability to extreme environment applications, SiGe HBTs are not immune to SEUs and are vulnerable to upsets even at low linear energy transfer rates. Therefore, there is a need in the industry for RHBD SiGe HBT circuitry capable of improved SEU immunity.